1. Field of the Invention
The present invention relates to a detection circuit configured to detect an open circuit of a load connected thereto.
2. Description of the Related Art
A related-art detection circuit is illustrated in FIG. 6. The related-art detection circuit includes a voltage input terminal 401, a voltage output terminal 402, an output transistor 403, a control circuit 404, a load open-circuit detection circuit 405 configured to detect an open circuit of a load connected to the voltage output terminal 402, and an output terminal 406 of the load open-circuit detection circuit 405.
The control circuit 404 controls the output transistor 403 to be turned on and off. When detecting an open circuit of a load connected to the voltage output terminal 402, the load open-circuit detection circuit 405 outputs a detection signal to the output terminal 406.
In the load open-circuit detection circuit 405, there is often employed a method involving monitoring a current of the output transistor 403, to thereby detect an open circuit of a load connected to the voltage output terminal 402. For example, a resistor 410 is connected between the voltage input terminal 401 and the output transistor 403, and whether a load is open or not is determined based on a voltage generated across both ends of the resistor 410. Under a state in which a load connected to the voltage output terminal 402 is open, no current flows through the output transistor 403, and hence an open circuit of a load connected to the voltage output terminal 402 is detected as described above.
The output transistor 403 is large in element size and input capacitance so that the output transistor 403 may cause large current to flow depending on a load connected to the voltage output terminal 402. It takes physical time to charge and discharge the large input capacitance of the output transistor 403 to control the output transistor 403 to be turned on and off, and hence it is difficult for the output transistor 403 to be turned on as soon as the detection circuit is powered on. Consequently, the output transistor 403 is still in an off state immediately after the detection circuit is powered on, and hence no voltage is generated at the resistor 410 even though a load is not actually open.
The related-art detection circuit illustrated in FIG. 6 therefore has a problem in that, immensely after the detection circuit is powered on, the load open-circuit detection circuit 405 erroneously determines that a voltage generated at the resistor 410 is small.